feat(install): add pre-flight environment and disk-target validation

archangel went straight from filesystem selection into a destructive install behind only a root check and a ZFS module load. A missing tool, a BIOS boot, a too-small or in-use disk, or a dead network surfaced as a confusing abort partway through, sometimes after partitioning had already run.

Two gates now fail fast. validate_environment runs after filesystem selection, before any disk is touched: it confirms UEFI boot mode and that every required command is present, with the list coming from a new required_commands helper built like pacstrap_packages. validate_install_targets runs after disk selection, before the first wipe: it refuses a target that's mounted, holds active swap, or belongs to an imported pool or md array, rejects disks under 20 GB, and confirms a mirror is reachable via DNS plus a TCP probe (no ICMP, since some networks drop it).

I folded the install_failure_cleanup hardening into the same change. It now falls back to lazy unmounts, so a pacstrap-interrupted target with busy bind mounts still releases the pool and unmounts the EFI partition. Without that, the disk-in-use guard would block the very retry the cleanup exists to enable. "Re-run to retry" only holds if the disk is genuinely freed first.

The 20 GB floor is decimal on purpose. It reads as the natural minimum and clears a 20 GiB disk image with headroom instead of sitting on the boundary.

1 files changed, 21 insertions, 0 deletions

diff --git a/installer/lib/common.sh b/installer/lib/common.sh
index 2cd4798..7998eeb 100644
--- a/installer/lib/common.sh
+++ b/installer/lib/common.sh
@@ -102,6 +102,27 @@ pacstrap_packages() {
     printf '%s\n' "${common[@]}" "${fs_specific[@]}"
 }
 
+# Print the external commands the installer needs for the given filesystem,
+# one per line: common partitioning/bootstrap tools first, then
+# filesystem-specific ones. validate_environment loops over these and
+# require_command's each, so a missing tool fails fast on the live ISO
+# instead of mid-install. Returns 1 for unknown filesystem.
+#
+# Usage: mapfile -t cmds < <(required_commands zfs)
+required_commands() {
+    local fs="$1"
+    local common=(
+        sgdisk wipefs partprobe mkfs.fat pacstrap
+    )
+    local fs_specific
+    case "$fs" in
+        zfs)   fs_specific=(zpool zfs) ;;
+        btrfs) fs_specific=(mkfs.btrfs grub-install) ;;
+        *)     return 1 ;;
+    esac
+    printf '%s\n' "${common[@]}" "${fs_specific[@]}"
+}
+
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